Mark two extension corruption related metrics as never expiring.

The two metrics are meant to monitor extension content verification
related stats:
ExtensionContentHashFetcher.CreateHashesTime
Extensions.CorruptExtensionTotalDisables
Mark these as never-expiring.

Bug: 976038, 976013
Test: None
Change-Id: I915898f9533a1e40a3576ce4924453ef9374cee8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1674206
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672104}
1 file changed